afternoon often brings rain at the water parks. what time do they close? if the goal is to "hit" a water park, we have had great success going about 3 hours before they close. by that time they've cleared out and you can get much more done in less time. My DD, from age 3 on has loved Blizzard Beach much more than TL because the kids area feels more adventurous to her (she's a daredevil).
If you have to go to MK on Sunday to fit it in, I would suggest doing rides in the morning, and saving the "show" type attractions for afternoon. I would definitely recommend EMH at magic kingdom--you will have a couple magical hours to treasure before it fills up. MY DD and I did fantasyland, then were waiting at the entrance to ToonTown. She ended up walking between Minnie and Mickey to open it, holding both their hands. We were first in Minnie's house; got the signatures of all the characters, got on the first ride of barnstormer and were out of there in time for our Buzz FP. And---it was the saturday of labor day weekend. By 1 pm the park was too full to bear